From McMaster University and the Henderson Research Centre, Hamilton, Ontario, Canada.

Grant Support: By the National Health Research Development Program of Health Canada (grant 6606-5620-400). AGEN Biomedical Ltd. donated the d-dimer kits. Drs. Kearon and Douketis are supported by the Heart and Stroke Foundation of Canada. Drs. Ginsberg is supported by the Heart and Stroke Foundation of Ontario. Drs. Crowther and Ginsberg are supported by the Canadian Institutes of Health Research. Dr. Bates is supported by the Canadian Institutes of Health Research, University–Industry Program. Dr. Lee is supported by the Canadian Institutes of Health Research, Drug Research and Development Program.

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Abstract

Background:

With suspected deep venous thrombosis and normal results on proximal vein ultrasonography, a negative d-dimer result may exclude thrombosis and a positive d-dimer result may be an indication for venography.

Objective:

To evaluate and compare the safety of 2 diagnostic strategies for deep venous thrombosis.

Erythrocyte agglutination d-dimer testing followed by no further testing if the result was negative and venography if the result was positive (experimental) or ultrasonography repeated after 1 week in all patients (control).

Nineteen of 408 patients (4.7%) in the d-dimer group and 3 of 402 patients (0.7%) in the repeated ultrasonography group initially received a diagnosis of deep venous thrombosis (P < 0.001). During follow-up of patients without a diagnosis of deep venous thrombosis on initial testing, 8 patients (2.1% [95% CI, 0.9% to 4.0%]) in the d-dimer group and 5 patients (1.3% [CI, 0.4% to 2.9%]) in the repeated ultrasonography group developed symptomatic venous thromboembolism (difference, 0.8 percentage point [CI, −1.1 to 2.9 percentage points]; P > 0.2). Venous thromboembolism occurred in 1.0% (CI, 0.2% to 2.8%) of those with a negative d-dimer result.

In outpatients with suspected deep venous thrombosis who initially had normal results on ultrasonography of the proximal veins, a strategy based on d-dimer testing followed by no further testing if the result was negative and venography if the result was positive had acceptable safety and did not differ from the safety of a strategy based on withholding anticoagulant therapy and routinely repeating ultrasonography after 1 week.